Electric eel power comes from cells, called electrocytes, that expel energy when needed. Eels can actually "synchronize the charging and discharging of thousands of cells in their bodies simultaneously," says Max Shtein, a chemical engineer at the University of Michigan who worked on research for a soft, flexible battery based on this concept. Shtein and his team, which included individuals from the University of Fribourg and the University of California, San Diego, attempted to replicate "the eel's physiology by creating about 2,500 units made of sodium and chloride dissolved in water-based hydrogels," all of which were printed out in rows resembling tiny buttons. They placed the charge-selective hydrogels on top and the saline and freshwater (blue) hydrogels below, for a reaction that actually delivered power. The prototype findings were published in the journal Nature last month. You can read more at Smithsonian magazine.